摘要： In this work, two small molecular electron acceptor (BT-FPDI and fBT-FPDI) comprising a central bithiophene (BT) bridge and two fused perylene diimide (FPDI) units were designed and synthesized for fullerene-free organic solar cells (OSCs). The molecular geometry of these electron acceptors can be adjusted through a locked conformation via photocyclization reaction. As expected, BT-FPDI has a highly twisted geometry with the assistance of the quasi-two-dimensional (quasi-2D) configuration of FPDI unit and modest dihedral angles between FPDI and BT units, while fBT-FPDI shows a relatively planar geometry with symmetrically aligned the FPDI wings. When pairing with polymer donor PTB7-Th, the intrinsic configuration characteristic of BT-FPDI guaranteed an impressive power conversion efficiency (PCE) of 8.07% with an open circuit voltage (Voc) of 0.81 V, and a recorded high short-circuit current density (Jsc) of 17.35 mA/cm2, which is almost the highest Jsc value reported in PDI-based fullerene-free OSCs. However, the optimal device employing fBT-FPDI as electron acceptor only delivered a PCE of 5.89% with a significantly reduced Jsc of 12.30 mA/cm2. The interesting result show that, unlike traditional PDI molecules, the ring-fusion molecular design has not produce the desired positive effect in FPDI derivatives, and also provide a new insight into the regulation of the molecular geometry based on FPDI acceptors with intrinsic quasi-2D structure.